Temperature responsive resistance control elements



April 30, 1963 L. MULDAWER 3,087,810

TEMPERATURE RESPONSIVE RESISTANCE CONTROL ELEMENTS Filed Nov. 24, 1959 RESISTANCE IN VEN TOR. LEONARD MULDAWER TEMPERATURE BY rp l ATTORNEY-3 United States Patent 3,087,810 TEMPERATURE RESPONSIVE RESISTANCE CONTROL ELEMENTS Leonard Muldawer, Bala Cynwyd, Pa., assignor to the United States of America as represented by the Secretary of the Army Filed Nov. 24, 1959, Ser. No. 855,242 2 Claims. (Cl. 75--165) This invention relates to metal alloys which undergo abrupt changes in resistance at predetermined temperatures and to the utilization of such changes to produce the various eifects of which an electric current is capable.

It is known that alloys of gold and cadmium undergo a phase change at a critical temperature (hereinafter designated as T which is dependent on the proportions of the two metals. It is also known that (1) this change in phase is accompanied by an abrupt change in the electrical resistance of the alloy, and (2) occurs at one temperature as the temperature is raised and at a slightly different temperature as the temperature is reduced. Thus an alloy such as Au 52.5 Cd 47.5 (the percentages being atomic) has a T at about 60 C. on cooling and about 75 C. on heating. An alloy Au Od has a T, at about 30 C. on cooling and about 35 C. on heating. The maximum range in T for pure AuCd alloys is therefore about 75 C. since alloys can be made over a 3 or 4% range.

The present invention extends the range of T values by the substitution of a third element. Thus by substituting silver for gold in various percentages, the T range can be extended to include temperatures from 75 to 160 C. Further extensions may be produced by substituting copper for gold or zinc for cadmium. Such extensions in the T range have the important advantage that a member made of the alloy may be made to undergo an abrupt change in electrical resistance at any temperature within a much wider range of temperatures than has been available heretofore.

The invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope is indicated by the appended claims.

Referring to the drawings:

FIG. 1 is a graph indicating the relation between the temperature and resistance of a gold-cadmium alloy containing Au A-g Cd these and all other alloy percentages mentioned herein being atomic,

FIG. 2 is a pair of curves indicating the relation between T and various percentages of silver substituted for gold in the alloy (Au, Ag) Cd The curve of FIG. 1 is based on data obtained from an alloy Au Ag Cd this alloy being in the form of a rod three inches long and one eighth inch in diameter. The resistance is plotted in microolnns and the ICC temperature in degrees centigrade. It can be seen that there is an abrupt change in resistance at about C. when the temperature is increased and at about 55 C. when the temperature is decreased. Obviously, if this rod is connected in a circuit including a source of electrical power, this abrupt change in resistance will produce a similar change in the current flowing through the circuit.

As will be apparent to those skilled in the art, the alloy has utility in numerous applications where an electric current is to be regulated by resistance change and without the use of switch contacts.

As indicated by the curves of FIG. 2, the temperature at which the abrupt change in resistance occurs may be at any temperature selected from a range which is greatly increased by the substitution of silver for various percentages of gold. In this figure, the percent of substituted silver in alloy (Au, Ag) Od is plotted against T The curve A represents the values of T when the temperature is increased and the curve B represents the values of I, when the temperature is decreased.

It can be seen that the substitution of silver for gold extends the T range down to about -160 C. As previously indicated, this range can be further extended by substituting copper for gold, zinc for cadmium or the like.

As can be seen from the foregoing description, the temperature responsive resistance control element of the present invention operates without contacts to vary the resistance of an electrical circuit and may be made to do this at any one of a wide range of temperatures.

I claim:

1. A temperature responsive resistance control element for electrical circuits having critical temperatures at which it undergoes an abrupt change in electrical resistance, said critical temperatures varying between about 160 C. and C., said element consisting essentially of about 47.5 atomic percent cadmium, about 151 atomic percent silver and about 15-515 atomic percent gold.

2. A temperature responsive resistance control element having critical temperatures at which it undergoes an abrupt change in electrical resistance, said critical temperatures being about C. and C. when said element is heated and cooled respectively through said critical temperatures, said element consisting essentially of 47.5 atomic percent cadmium, about 51 atomic percent silver and about 1.5 atomic percent gold.

References Cited in the file of this patent UNITED STATES PATENTS 2,371,240 Hensel et al. Mar. 13, 1945 2,550,344 Godshalk Apr. 24, 1951 2,949,594 Tava et al. Aug. 16, 1960 

2. A TEMPERATURE RESPONSIVE RESISTANCE CONTROL ELEMENT HAVING CRITICAL TEMPETRATURES AT WHICH IT UNDERGOES AN ABRUPT CHANGE IN ELECTRICAL RESISTANCE, SAID CRITICAL TEMPERATURES BEING ABOUT -150* C. AND 160*C WHEN SAID ELEMENT IS HEATED AND COOLED RESPECTIVELY THROUGH SAID CRITICAL TEMPERATURES, SAID ELEMENT CONSISTING ESSENTIALLY OF 47.5 ATOMIC PERRCENT CADMIUM, ABOUT 51 ATOMIC PERCENT SILVER AND ABOUT 1.5 ATOMIC PERCENT GOLD. 